Thermal Barrier Coating

ABSTRACT

A coated substrate has a substrate and a coating system having one or more ceramic layers. At least a first layer of one of the one or more ceramic layers is a columnar layer having as-deposited columns and intercolumn gaps. The intercolumn gaps have a mean width at least one of: at least 4.0 micrometers; and at least 1.5% of a thickness of said first layer.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. patent application Ser. No. 63/016,203, filedApr. 27, 2020, and entitled “Thermal Barrier Coating”, the disclosure ofwhich is incorporated by reference herein in its entirety as if setforth at length.

BACKGROUND

The disclosure relates to gas turbine engine ceramic thermal barriercoatings (TBC). More particularly, the disclosure relates to coatingssubject to calcium-magnesium-alumino-silicate (CMAS—also known as“molten sand attack”) contaminants in the hot sections of the engine.

Gas turbine engines (used in propulsion and power applications andbroadly inclusive of turbojets, turboprops, turbofans, turboshafts,industrial gas turbines, and the like) include ceramic coatings used asthermal barrier coatings (TBC), environmental barrier coatings (EBC),abradable coatings, and the like. Principal application techniquesinclude electron beam physical vapor deposition(EB-PVD) and air plasmaspray (APS). Principal ceramic materials are stabilized zirconias,namely yttria-stabilized zirconia (YSZ) and gadolinia-stabilizedzirconia (alternatively known as GdZ, GSZ, or GZO).

Particularly with YSZ, EB-PVD tends to produce a crystal-like columnarstructure.

APS tends to produce a splatted structure. Suspension plasma spray (SPS)tends to yield an equiaxed columnar structure as compared to the singlecrystal columns produced in EB-PVD. The EB-PVD columns have sharper andless varied boundaries with little bridging between columns compared toSPS.

There have been many proposals for addressing CMAS. Some involveapplying a dense sealing layer or topcoat over a more conventional TBClayer to prevent infiltration. Others involve applying a reactivelayer/topcoat which reacts with CMAS to prevent further infiltration.

United States Patent Application Publication 20190078215A1 (the '215publication), of Wessels et al., Mar. 14, 2019, “CMAS-Resistant ThermalBarrier Coating and Method of Making a Coating thereof”, the disclosureof which is incorporated by reference in its entirety herein as if setforth at length, discloses deep prior art SPS coatings as havinginter-columnar gaps subject to CMAS infiltration. The '215 publicationdiscloses combatting CMAS infiltration by reducing gap width to below 5micrometers.

SUMMARY

One aspect of the disclosure involves a coated substrate comprising: asubstrate; and a coating system comprising one or more ceramic layers.At least a first layer of one of the one or more ceramic layers is acolumnar layer having as-deposited columns and intercolumn gaps. Theintercolumn gaps have a mean width at least one of: at least 4.0micrometers; and at least 1.5% of a thickness of said first layer.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively: said intercolumn gaps have a meanwidth of at least 4.0 micrometers over an area of at least 4.0 cm².

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively: the substrate is a metallicsubstrate; and the coating system comprises a bondcoat and said one ormore ceramic layers atop the bondcoat.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, one or more of: the metallicsubstrate is a nickel-based superalloy; the coated metallic substrate isa gas turbine engine component; the bondcoat is an MCrAlY or analuminide; and the first layer is a YSZ (e.g., 7 YSZ or 8 YSZ) or a GSZ(e.g., 59 GdZ).

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively: the metallic substrate is anickel-based superalloy; the coated metallic substrate is a gas turbineengine component; the bondcoat is an MCrAlY or an aluminide; and thecolumnar layer is a YSZ or a GSZ.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively: the metallic substrate is anickel-based superalloy; the coated metallic substrate is a gas turbineengine component; the bondcoat is an MCrAlY; and the columnar layer is aYSZ layer or a GSZ layer atop a YSZ layer.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the gaps are as-sprayed gaps.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the intercolumn gaps have mean depthsof at least 100 micrometers and the mean gap width is 4.0 micrometers to25.0 micrometers.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the coated substrate of is a gasturbine engine component and the columnar layer is along agaspath-facing surface of the component.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the substrate is grooved and thecoating system has open structures above the grooves.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the method comprises: applying thecolumnar layer by suspension plasma spray.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the method further comprises applyinga bondcoat to the substrate prior to the applying of the columnar layer.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the method further comprises:roughening the substrate or a bondcoat thereon prior to the applying ofthe columnar layer.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the roughening is an abrasiveprocess.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the abrasive process comprisesabrasive belting in two directions.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, a method for using the coatedsubstrate comprises running the coated substrate in a gas turbine engineexposing the coated substrate to CMAS. The exposing causes CMAS to enterthe gaps and laterally infiltrate into the columnar layer while leavingthe gaps open adjacent the infiltration.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the CMAS bridges gap openings whileleaving gap portions therebelow open.

A further aspect of the disclosure involves, a method for manufacturinga coated substrate. The method comprises: abrasive roughening of thesubstrate; applying a bondcoat to the substrate; and applying a ceramiccoating layer by suspension plasma spray.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the abrasive roughening comprisesabrasive belting directions.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the abrasive belting comprisesabrasive belting in two directions.

In a further embodiment of any of the foregoing embodiments,additionally and/or alternatively, the abrasive belting comprises:abrasive belting with a 120-mesh or coarser grit.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a coated substrate.

FIG. 1A is an enlarged schematic view of columns in a primary coatinglayer of the FIG. 1 coated substrate.

FIG. 2 is a schematic sectional view of the FIG. 1A coated substratein-service.

FIG. 3 is a further schematic sectional view of the FIG. 1 coatedsubstrate in-service.

FIG. 4 is a thresholded diagram made from a sectional micrograph of abaseline coated substrate.

FIG. 4A is an enlarged view of a column in a primary coating layer ofthe FIG. 3 coated substrate.

FIG. 5 is a thresholded diagram made from a sectional micrograph of afirst example coated substrate.

FIG. 5A is an enlarged view of a column in a primary coating layer ofthe FIG. 5 coated substrate.

FIG. 6 is a thresholded diagram made from a sectional micrograph of asecond example coated substrate.

FIG. 6A is an enlarged view of a column in a primary coating layer ofthe FIG. 6 coated substrate.

FIG. 7 is a thresholded diagram made from a sectional micrograph of athird example coated substrate.

FIG. 7A is an enlarged view of a column in a primary coating layer ofthe FIG. 7 coated substrate.

FIG. 8 is a thresholded diagram made from a sectional micrograph of afourth example coated substrate.

FIG. 8A is an enlarged view of a column in a primary coating layer ofthe FIG. 8 coated substrate.

FIG. 9 is a thresholded diagram made from a sectional micrograph of afifth example coated substrate.

FIG. 9A is an enlarged view of a column in a primary coating layer ofthe FIG. 9 coated substrate.

FIG. 10 is a plot of total porosity against particle velocity for fournozzle diameters.

FIG. 11 is a plot of porosity less than two micrometers versus particlevelocity for the FIG. 10 nozzles.

FIG. 12 is a plot of porosity more than two micrometers versus particlevelocity for the FIG. 10 nozzles.

FIG. 13 is a sectional micrograph of an SPS-coated first roughenedsubstrate.

FIG. 14 is a thresholded surface view of an SPS-coated second roughenedsubstrate.

FIG. 15 is a thresholded surface view of an SPS-coated third roughenedsubstrate.

FIG. 16 is a black/white thresholded image of the FIG. 4 sourcemicrograph with an overlay of measurement lines.

FIG. 17 is a histogram of the column gap widths measured at the FIG. 16measurement lines.

FIG. 18 is a black/white thresholded image of the FIG. 7 sourcemicrograph with an overlay of measurement lines.

FIG. 19 is a histogram of the column gap widths measured at the FIG. 18measurement lines.

FIG. 20 is a black/white thresholded image of the FIG. 8 sourcemicrograph with an overlay of measurement lines.

FIG. 21 is a histogram of the column gap widths measured at the FIG. 20measurement lines.

FIG. 22 is a black/white thresholded image of the FIG. 9 sourcemicrograph with an overlay of measurement lines.

FIG. 23 is a histogram of the column gap widths measured at the FIG. 22measurement lines.

FIG. 24 is a drawing of an initial annotated micrograph highlightingcolumn features in a single solid color represented by hatching in thedrawing.

FIG. 25 is a drawing of the annotated image cropped back to originalimage size.

FIG. 26 is a preliminary binary mask processed from the annotated image.

FIG. 27 is drawing of a cleaned and color-tagged low fidelity mask.

FIG. 28 is a drawing of an overlay view of the low fidelity mask on theoriginal image.

FIG. 29 is a view of an image subtracting the low fidelity mask from theoriginal image.

FIG. 30 is a view of a mask regenerated from the low fidelity mask basedupon allocation of the subtracted pixels.

FIG. 31 is a view of a mask generated by eroding the pixel-correctedmask of FIG. 30 .

FIG. 32 is a view of the final binary mask generated from the erodedmask of FIG. 31 .

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

With a traditional YSZ EB-PVD columnar structure, the narrowinter-column gaps allow the coating to be rapidly infiltrated by CMAS.Capillary action of low viscosity molten CMAS results in rapidinfiltration velocities in column gaps that are about 1 micrometer insize. EB-PVD columns are dense with exception of feather structure onouter periphery. The elastic energy per area of coating associated withthermal stress achieved by cooling a TBC-coated substrate where the TBCand substrate have different thermal expansion coefficients is dictatedby the modulus of and thickness of the TBC layer. CMAS infiltration intothe TBC structure effectively increases the coating modulus of theinfiltrated thickness which raises the elastic energy. The elasticenergy increases as a function of the thickness of the CMAS-infiltratedhigher modulus layer. Therefore the TBC spallation life when infiltratedby CMAS is dictated by the depth of CMAS infiltration (inversely) andthe toughness of the EB-PVD column. See, Carlos Levi, John Hutchinson,Marei-hélène Vidal-Séetif, & Curtis Johnson, (2012). “EnvironmentalDegradation of TBCs by Molten Deposits”, MRS Bulletin, October, 2012,Volume 37, Pages 932-941, 934, Materials Research Society, Pittsburgh,Pa.

APS splat structures are infiltrated by CMAS through similar capillaryaction of low viscosity molten CMAS. Inter-splat structure createstortuous infiltration path with varied splat and pore sizes resulting inlonger infiltration paths than EB-PVD. Additionally the thermal gradientin APS coatings is greater than EB-PVD due to the lower thermalconductivity (associated with APS porosity being generally perpendicularto the direction of heat transport). Assuming the APS and EB-PVDcoatings were operating at the same surface temperatures the thicknessof a CMAS-infiltrated layer would be thinner in the APS case. However,the weak bonding between splats in APS has a substantially lowertoughness when compared with the continuous single crystal columns inEB-PVD. Therefore the relatively low TBC life under

CMAS conditions in APS coatings is caused by the low intersplatstrength.

Suspension plasma spray (SPS) tends to yield a columnar structure.Relative to EB-PVD columns, SPS columns are wider, with greater and moreinconsistent gap openings, and are formed by consolidation of individualthermal spray splats in an equiaxed structure. SPS column widths are onthe order of ˜100 micrometers in diameter as compared to ˜10 micrometersfor EB-PVD. The gap sizes between EB-PVD columns are approximately 1micrometer while that between SPS columns is larger and more variedranging from 1 to greater than 10 micrometers. The SPS columnarstructure consists of a compilation of fine splats on the order of a fewmicrometers each that accumulate into columns.

Also, the SPS splat structure may have a wide distribution of pore sizes(of pores formed between the depositing splats) for given sprayparameters and the parameters may be selected to further tailor thatdistribution. The pore structure within the columns is largerinterconnected and open to the column surface as documented by Klement,U., Ekberg, J. & Kelly, S. T. “3D Analysis of Porosity in a CeramicCoating Using X-ray Microscopy”, J Therm Spray Tech,. Volume 26, pages456-463,Jan. 31 2017, Springer, New York, N.Y. As noted in the '215publication, typical SPS columns have inter-columnar gaps subject toCMAS infiltration. The '215 publication discloses combatting CMASinfiltration by reducing gap width to below 5 micrometers.

As an alternative to the reduced gap width of the '215 publication, anincreased gap width can provide an alternative mechanism for combattingCMAS damage to SPS thermal barrier coatings. FIG. 1 shows a coatedarticle 20. The article comprises a substrate 22 having a surface 24.The exemplary substrates are metallic (e.g. nickel-based superalloy,cobalt-based superalloy, or the like, typically a casting). Alternativesubstrates are monolithic ceramics, ceramic matrix composites(CMC)(e.g., SiC—SiC), and the like. The coated article further includesa thermal barrier coating system (coating system) 26 atop the substrate.Broadly, exemplary articles are hot section components of gas turbineengines and the coating system 26 may be along gaspath—facing surfacesof such components. Exemplary components are blades (with the airfoilpressure side and suction side surfaces, platform outer diameter (OD)surface being key), vanes (with the airfoil pressure side and suctionside surfaces, inner diameter (ID) shroud OD surface, and OD shroud IDsurface being key), bulkheads, combustor panels, struts, and the like.Further variations are to produce abradable coatings on the innerdiameter surface of blade outer airseals (BOAS) where the porosityincrease may improve abradability.

The coating system 26 may include a bondcoat 28. The presence, material,and application technique of the bondcoat may be dependent on theparticular substrate and use and may reflect any of numerous prior artor yet-developed bondcoats. The exemplary bondcoats are metallic (e.g.,MCrAlY). Alternatives are aluminides (e.g., diffusion aluminides). Theexemplary bondcoat 28 is shown having an outer surface 30. The coatingsystem 26 further includes a thermal barrier coating (TBC) 32. Theexemplary TBC is a two-layer TBC with a first layer (base layer) 34 atopthe bondcoat 28 and a second layer (primary layer) 38 atop an outersurface 36 of the base layer 34 and extending to an outer surface 40.

In this example, the second layer 38 is “main” or “primary” in that itrepresents the thickest layer within the coating system 26 and TBC 32and, more particularly, may represent a majority of the thickness ofboth said coating system 26 and TBC 32. For purposes of illustration,the coating system 26 has a thickness T, the bondcoat a thicknessT_(BC), the TBC a thickness T_(TBC), the base layer 34 a thickness T₁,and the primary layer a thickness T₂.

As is discussed further below, the primary layer 38 has a columnarstructure characteristic of application by suspension plasma spray (SPS)(e.g., powder ceramic feedstock in an ethanol carrier). In thisparticular example, the base layer 34 is also a columnar SPS layer. Insuch an exemplary situation, the columns span both layers with the baselayer providing a proximal portion of many columns and the main layerforming distal portions. In alternative embodiments, the base layer maybe non-columnar with the columns formed only in the main layer. In yetalternative embodiments, there is a single ceramic layer being an SPScolumnar layer. Individual columns 50 extend from roots 52 to tips 54and have lateral surfaces (sides) 56. Gaps 60 may separate the columns.FIG. 1 further shows column width W_(C), gap width W_(G), and gap heightH_(G) between gap bases 62 and the column tips 54. In the exemplaryembodiment, H_(G) is essentially the same as T_(TBC). As is discussedfurther below, spray deposition parameters are selected to broaden gapwidth WG contrary to conventional wisdom.

For example, a reduced droplet size present in the plume would result ina greater influence by the gas stream on particle (droplet) trajectoryas it approached the target surface. This means a smaller droplet willhave a shallower average impingement angle with the substrate whichwould result in a greater shadowing effect from neighboring columns andtherefore and increased gap size. Droplet size can be reduced throughmultiple methods including higher gas velocity, lower suspensionviscosity, and lower suspension surface tension.

Also, increasing surface roughness (discussed further below) increasesthe shadowing effects that create the separation of columns. Increasedsurface roughness can be through different grit blasting intensities(e.g., after bondcoat application) or by creating a larger scale surfacetexture (coarse abrasive belting, milling, knurling, laser etching, orthe like either before or after bondcoat application).

More broadly, the gaps 60 represent inter-column porosity. Theparticular disordered nature of column formation often means that thereis great variation in gap width and intermittent bridging of the gapsbetween columns. However, the distinct columnar structure is stillvisible in micrographic section.

Additionally, there is intra-column porosity. FIG. 1A shows internalpores 70 within the columns 50. The distribution and size of the pores70 (e.g., individual pore size and overall intra-column porosity) mayalso be a relevant consideration. Instead of being selected to resistlateral infiltration of CMAS, the size and distribution of the pores 70may be selected to draw CMAS laterally into the columns to resistnarrowing and filling of the gaps. By drawing the CMAS laterally intothe columns and out of the column gaps, the elastic modulus of theinfiltrated coating does not increase significantly.

FIGS. 2 and 3 show the article 20 after service in a CMAS-inducingenvironment with a CMAS accumulation 100 atop the TBC 32. FIG. 3represents a later stage after greater CMAS exposure. The exemplaryaccumulation 100 is shown having an outer surface 102 and, at least bythe FIG. 3 service duration, having portions bridging the gap 60openings 64. The relatively large width of the gaps 60 reduces thecapillary driving force for CMAS infiltration. Additionally, theintra-column porosity may laterally draw out from the gaps 60 CMAS thathas infiltrated, leaving respective intra-column cavities formed by thegaps 60 beneath the CMAS accumulation 100. This dynamic of reducedinfiltration and improved lateral exfiltration from the gaps 60 mayincrease the service life. Eventually, as the intra-column pores 70 fill(becoming filled pores 70′), the exfiltration will slow and the gaps 60will eventually fill (stage not shown) and the coating will fail.

The intra-column porosity 70 may, thus, be configured to delay the timebefore the gaps begin to fill. The gap filling will increase the modulusof the infiltrated layer and drive spallation.

FIG. 3 further shows the thickness T_(CMAS) of the accumulation 100 atthe gaps. T_(CMAS) is the vertical height of the portion of anindividual gap that has been filled and bridged by CMAS. The averagevalues of all T_(CMAS) can describe the layer that will act as acontinuous material with higher in-plane modulus that the coating ofFIG. 1 . This continuous T_(CMAS) layer with its high modulus willincrease the total stress on the coatings system. Once the averageT_(CMAS) reaches a critical threshold, spallation of the partial orcomplete coating thickness will occur. The time to reach this criticalTCMAS thickness is dependent on the coating material propertiesincluding toughness and modulus but also on the size of the gap 60openings 64 and the volume of porosity 70 that can exfiltrate CMAS fromgaps 60.

FIG. 4 shows a baseline TBC 932 having a base layer 34 and a primarylayer 938. FIG. 4 is a thresholded version of a grayscale micrographused for reproducibility herein. In general, black spots in the primarylayer 938 will correspond to porosity. Due to chemistry and/orapplication technique differences, the base layer will be darker on themicrograph. At the level of thresholding appropriate to show porosity inthe primary layer, the darker color of the base layer yieldsdisproportionate blackness in the thresholded image. Thus the base layerin the thresholded image appears to have greater porosity thant heprimary layer even though it has much lower actual porosity and porosityvisible in the source micrograph. The base layers in micrographs belowsuffer similar distortion via the thresholding. Further examplesdiscussed below preserve the base layer 34 and change parameters of theprimary layer. Yet other examples may change parameters of the baselayer. The distinct columns 950 are visible as are gaps between.However, the gaps vary between heavily bridged (e.g., the two columns inthe left of the view) and much less bridged (between the right of thosetwo columns and the next column). Typical gap width may be in thevicinity of 2 micrometers to 3 micrometers and may be determined viaimage analysis.

An exemplary gap measurement process involves image thresholding andanalysis of the thresholded image. FIG. 16 shows a black/whitethresholded version of the FIG. 4 micrograph image.

Several examples of preparing the thresholded image may involve a neuralnetwork implementation. The neural network implementation may be basedon learning from manual iterations. For example, in a manual iteration,the technician may take an image, tag individual columns or individualcolumn objects (where columns have different protrusions out of theimage plane so that one apparent segmented column is formed by multipleactual columns). The manual operation may then turn the column-selectedimage into a binary mask. The technician may apply the line array andperform analysis. However, this is particularly optional as theapplication of the array and the analysis may more easily be directlyprogrammed than the initial identification of columns. In the manual orautomated process, the column widths are then tallied.

In an example of the process, in a first step, a technician loads theimage into image processing software (e.g., written in the Pythonprogramming language of the Python Software Foundation, Beaverton,Oregon). In one example, the image is a 3-channel (RGB) image.

In a second step (which may precede, follow or occur simultaneously),the technician loads the image into some form of graphical program (animage editor, a presentation program such as Microsoft Corporation'sPowerPoint presentation software, or the like). The technician using thegraphical program, manually annotates the images to outline and segmentindividual column features (columns or separate sections of columnsdepicted in the image). The annotation may draw shapes just within theboundary of each column feature/segment. The technician fills the shapeswith a color fill (e.g., pure yellow color (RGB=[255,255,0]) in anexample). Edge color is assigned as black. In the PowerPoint softwareexample, the background image plus all the yellow filled column segmentshapes are selected and grouped together as single image (“Group All”)by the technician. The grouped image (FIG. 24 ) is now saved by thetechnician as a new image. For purposes of reproducibility herein, theFIG. 24 (also FIG. 25 ) representation shows hatching on a line drawingwhere the solid color would be on the micrograph.

If some of the manually added shapes extend past the border of theoriginal image, the technician crops the “grouped” image using thedimensions of the original image so that they are the same size (FIG. 25).

Then the technician loads the grouped image into the image processingsoftware.

The image processing software script applies simple thresholding forcolored (yellow in the example) pixels to find and separate all shapesas distinct objects and create a single binary mask (i.e., indicating acolumn or not) (FIG. 26 ). There are usually some small artifacts thatare created either by overlapping power point shapes or Python, so thePython script cleans up the image to remove these small artifacts thatare below a certain size limit (FIG. 27 ). In the example, the scriptalso assigns a unique color to each column object to aid viewing. Forpurposes of illustration, FIG. 27 labels colors of the image with labelsC1-C17.

For visualization, the script overlays the processed low fidelity maskon the original image (FIG. 28 ). Such a result may appear acceptablebut may typically be missing about 5-10% of the columns, especially atthe borders (image edges). Thus, discussed below, a further higherfidelity mask may be generated for improved accuracy. In this example,the script or technician also assigns colors to aid viewing. Forpurposes of illustration, FIG. 28 labels colors of the image with labelsC21-C37. These may be the same (or similar) to C1-C17 or different. FIG.28 also show solid line borders of the coloration within the columns.

To create higher fidelity masks, the script applies grayscale pixelthreshold that finds all pixels above the substrate/bondcoat or baselayer (if any) that are part of the primary layer. The script thensubtracts from the initial image the pixels that have already beenlabeled in the low fidelity mask (FIG. 29 ). The script then assignsunclassified pixels to the closest column object by Euclidean distance(FIG. 30 ).

At this stage the resulting mask labels are very closely abutting andsometimes there are small floating islands (e.g., artifacts of anout-of-plane column) that should not be included as part of a coatingcolumn object in the mask. So the script again removes small artifactsto remove this noise. Then the script subjects each column object to abinary erosion operation which shrinks the corresponding mask portion bya certain size, increasing separation between neighboring columns (FIG.31 ).

At this point, there is 2D array where the pixel color corresponds tounique object identifier number. For instance, all pixels that are zero(black) belong to the background. All pixels of 1 (white) belong to asingle column object, and so forth for each remaining object and itscolor. A simple threshold operation (pixel value>0) will generate abinary coating column mask (FIG. 32 ) which is used for analysis likethe coating column gap width assessment.

Once the binary mask is processed using the workflow discussed above,the script then places the N equally spaced lines between the upperlimit and lower limit of the primary layer minus a certain buffer area.As noted above, this buffer area is introduced to avoid measuring asgaps open spaces that are not actually gaps.

Because the script measures distance between consecutive white pixelsalong each line (i.e., the width of the black space between columns), itis important to make sure each line starts and ends in a column objector white pixel to not over-estimate gaps based upon removed columnportions at the two borders.

Thus, each line consists of a series of 0's and 1's, where the 1indicates the pixel is in a column object and 0 if it is not. Next, thescript calculates the difference between consecutive values—whichresults in zero if nothing changes and ±1 if it changes from 0 to 1 or 1to 0. Using the coordinates of these inflection points, the scriptdirectly calculates gap spacing which the script converts from pixelunits to a linear dimension (e.g., micrometers) with the correspondingscale factor.

FIG. 16 also includes an array of straight measurement lines parallel tothe general substrate surface. Gap widths along each line are measured(via programmed analytical tools). In this exemplary embodiment, thelines are at an even spacing starting from a lowermost line spacedslightly above the substrate to an uppermost line just below theterminal openings of the lowest gap. The exemplary spacing is 5.0micrometers. An exemplary line count is a matter of choice, but 1.0 to20.0 micrometers spacing would be illustrative for typical uses.

Even a single line may be used and, at the other end, an upper end online count is limited only by desired expenditure of labor and computinghours as well as image resolution. Thus, an exemplary range is 1 to 100lines, more particularly, 10 to 100 lines or 10 to 50 lines.

FIG. 17 is a histogram of gap widths. The X axis shows gap width inmicrometers. The Y axis is a fraction of the number of gaps of a givenwidth. In this example, the mean gap width is 2.4 micrometers (which isabout 1% of the layer thickness) based on gap count rather than beingweighted by gap width. The min. gap width is 0.3 micrometers, the max.gap width is 29.1 micrometers, the twenty-fifth percentile gap width is1.3 micrometers, and the seventy-fifth percentile gap width is 2.6micrometers.

FIG. 4A shows intra-column porosity. In particular, there is a totalamount of porosity volume (seen as area in micrograph cross-section)present composed of a range of different pore sizes. There are a smallnumber of pores with greater than 2 square micrometers area (cut planesection) and a large number of pores with less than 2 square micrometersarea. The larger pores tend to be associated with (e.g., immediatelyadjacent to) the gap structure between the columns while the smallerpores are generally formed between individual splats in the columns.Application parameters for the TBC 932 and additional examples are shownin Table I. In particular, Table I shows parameters for the baseline ofFIG. 4 , five tested examples of FIGS. 5-9 , and additional specificembodiments and ranges. In the baseline and five examples, the gun usedfor both layers was a 100HE™ plasma spray system of Progressive Surface,Grand Rapids, Mich. The first layer of material was a YSZ, namely, 8YSZ.The second layer of material was a GdZ, namely, 59 wt. percent gadoliniain zirconia (59 Gdz). The base layer thickness T₁ was approximately 65micrometers. The primary layer thickness T₂ was approximately 260micrometers. As is discussed further below, the examples reflect changes(relative to the baseline) in one or more of power, total gas flow rate,gas composition (relative concentration/rates of argon, hydrogen, andnitrogen), suspension feed rate, nozzle exit diameter, and gun standoff.An exemplary T₂ range is 100 micrometers to 400 micrometers

In various implementations, parameters of the particular guns used willinfluence power, flow rate, feed rate, standoff, etc. Nevertheless,similar modifications may be made to baseline processes using other gunsand other baseline parameters. Furthermore, yet other modifications maybe made.

TABLE I 1st (Base) Layer (optional) Feed Nozzle rate exit Power Ar H₂ N₂(ml/ Standoff Ex/ (in) Material (kW) (scfh) (scfh) (scfh) min) (in)Baseline 0.375 8YSZ 105 180 120 120 90 2.75 Ex. 1 0.375 8YSZ 105 180 120120 90 2.75 Ex. 2 0.450 8YSZ 105 180 120 120 90 2.75 Ex. 3 0.375 8YSZ105 180 120 120 90 2.75 Ex. 4 0.375 8YSZ 105 180 120 120 90 2.75 Ex. 50.375 8YSZ 105 180 120 120 90 2.75 Range 1A 0.375 8YSZ 105 180 120 12090 2.75 Range 1B 0.375 8YSZ 105 180 120 120 90 2.75 Range 1C 0.375 8YSZ105 180 120 120 90 2.75 Range 2A 0.375 8YSZ 105 180 120 120 90 2.75Range 2B 0.375 8YSZ 105 180 120 120 90 2.75 Range 2C 0.375 8YSZ 105 180120 120 90 2.75 Range 3A Range 3B Range 3C Range 4A Range 4B Range 4C2nd (Primary) Layer Feed Total rate gas Power Ar H₂ N₂ (ml/ Standoffflow Ex/ Material (kW) (scfh) (scfh) (scfh) min) (in) (scfh) Baseline59GdZ 95 180 120 120 90 3.00 420 Ex. 1 59GdZ 95 120 80 80 90 3.00 280Ex. 2 59GdZ 95 220 80 80 90 3.00 380 Ex. 3 59GdZ 85 120 120 120 90 3.50360 Ex. 4 59GdZ 95 300 120 120 90 3.00 540 Ex. 5 59GdZ 95 180 120 120 453.00 420 Range 1A 59GdZ  70-105 100-180  60-160  60-160 10-90 2.75-4.50220-420 Range 1B 59GdZ 75-95 120-180  60-120  60-120 10-90 2.75-4.50240-420 Range 1C 59GdZ 75-95 120-180  80-120  80-120 25-90 2.75-4.00280-420 Range 2A 59GdZ  70-105 120-400  80-160  80-160 10-90 3.00-4.50420-640 Range 2B 59GdZ  70-105 200-400  80-160  80-160 10-90 3.00-4.50440-640 Range 2C 59GdZ  70-105 240-400 100-160 100-160 25-90 3.00-4.00480-640 Range 3A 8YSZ  80-105 100-180  60-160  60-160 10-90 2.75-4.50220-420 Range 3B 8YSZ  85-105 120-180  60-120  60-120 10-90 2.75-4.50240-420 Range 3C 8YSZ  85-105 120-180  80-120  80-120 25-90 2.75-4.00280-420 Range 4A 8YSZ  80-105 120-400  80-160  80-160 10-90 2.75-4.50420-640 Range 4B 8YSZ  80-105 200-400  80-160  80-160 10-90 2.75-4.50440-640 Range 4C 8YSZ  80-105 240-400 100-160 100-160 25-90 2.75-4.00480-640

Other YSZ and GdZ may be used in place of the 8YSZ and 59 GdZ. Inparticular, 7YSZ would be fully substitutable for 8YSZ.

The Table I Range 1A-C and Range 3A-C ranges feature less total gas flowper gun exit area to reduce particle velocity and increase intracolumnporosity primarily. Lower power and greater standoff can additionallyincrease intracolumn porosity. Lower feed rate can increase gap size anddecrease average column diameter.

The Table I Range 2A-C and Range 4A-C ranges increase total gas flow pergun exit area to increase gap size but reduce total porosity. Reductionin power and increased standoff will recover or increase intracolumnporosity due to lower particle temperature at point of deposition.

Further variations may involve modifying the base layer (if present).One group of variations involves seeking to alter it similarly to theprimary layer. For example, the modified YSZ parameters of the Range 3or 4 families may be used for a base layer covered by a GdZ second layeraccording to the Range 1 or 2 families. Nevertheless, toughness or otherfactors may favor use of the baseline YSZ base layer because, due totemperature gradient across the coating thickness, CMAS infiltration inlower depths may be less of a problem. In that vein, The baseline YSZbase layer may also be used with the Range 3 or 4 family primary layer.

FIG. 5 shows the effect of reduced particle velocity relative to thebaseline. In this example, it is achieved by merely evenly reducing flowrates by one third and maintaining other parameters. The mostsignificant result is an increase in intra-column porosity (FIG. 5Aversus FIG. 4A). In particular, total porosity increased from about 20%to about 32% as measured by image analysis from micrographs at 250xmagnification. The fraction of pores greater than 2 square micrometers(of sectional area) increased from about 13% (66% of the total porosity(in sectional area)) to about 25% (79% of porosity), while the poresless than 2 square micrometers decreased minimally from 7.0% to 6.8% (ofsectional area). Additionally, the average column diameter remainedapproximately similar.

FIG. 6 shows an alternative mechanism for reducing particle velocity byincreasing the nozzle exit diameter while also reducing net gas flow. Inthis particular example, the gas composition is changed to haverelatively high argon. The increased fraction of the inert argon in thegas reduces the heat addition from use of nitrogen and hydrogen in theplasma. A relatively heavy gas like argon maintains or increasesparticle velocity. Intra-column porosity is also increased relative tothe baseline. Gap size is generally similar to the baseline or slightlyincreased.

FIGS. 7-9 discussed below reflect other parameter changes. FIGS. 18, 20,and 22 are respective corresponding thresholded images like FIG. 16 andFIGS. 19, 21, and 23 are respective corresponding histograms like FIG.17 . Table II provides the measured gap width:

TABLE II Gap Width (micrometers) FIG. Mean Min 25% 75% Max 4 (prior art)2.4 0.3 1.3  2.6 29.1 7 5.4 0.3 2.0  7.4 39.7 8 8.4 0.4 3.3 10.9 73.2 95.8 0.3 2.6  7.5 38.9

FIG. 7 shows reduced power, increased standoff, and reduced volumetricflow. In this example, the relative argon content is reduced.Intra-column porosity is increased relative to the baseline. Inparticular, total porosity increased to about 28% as measured by imageanalysis from micrographs at 250x magnification. The fraction of poresgreater than 2 square micrometers increased to about 22% (of sectionalarea), while the pores less than 2 square micrometers decreased to 6.3%.Gaps and gap sizes are less defined because of the increase in the largepores (those greater than 2 square micrometers) at the periphery of thecolumns and because of associated increased bridging. Average gap sizewas measured to be 5.4 micrometers which is about 2 percent of layerthickness.

FIG. 8 shows the effect of increased particle velocity relative to thebaseline. In this example, it is achieved by increasing the argon flowrate. The gap width is significantly increased. Total porosity isdecreased to about 18% as measured by image analysis from micrographs at250x magnification. The fraction of pores greater than 2 squaremicrometers (of sectional area) decreased to about 12%, while the poresless than 2 square micrometers decreased to 5.9%. Average gap size isincreased to 8.4 micrometers.

FIG. 9 shows effects of decreasing feed rate while maintaining otherparameters. Relative to the baseline, porosity is increased to about 26%as measured by image analysis from micrographs at 250x magnification.The pores greater than 2 square micrometers (of sectional area)increased to about 18%, while the pores less than 2 square micrometersincreased to 8.3%. Relative to the baseline, column width is decreased,resulting in increased gap frequency. The gap size increased to 5.8micrometers.

FIG. 10 is a plot of total porosity versus particle velocity for fournozzle diameters. Particle velocity was varied from approximately 200m/sec to greater than 600 m/sec as measured by a Tecnar Accuraspray g3cplume diagnostic sensor (Tecnar Automation Ltée,Saint-Bruno-de-Montarville, Quebec, Canada) at a standoff distance of3.25 inches. Total porosity and pores greater than 2 square micrometersdecrease as a function of particle velocity. Parameters varied toachieve the velocities were the total gas flow and the ratios of gasesused.

FIGS. 11 and 12 respectively break out the porosity less than twomicrometers and porosity greater than two micrometers. The size ismeasured by image analysis from micrographs at 250× magnification.

From FIGS. 10-12 , it is seen that the results collapse to a singletrend of porosity as a function of particle velocity.

Thus, it is seen that spray parameters alone may be used to achieve asignificant gap width increase. An exemplary range of mean width is 4.0micrometers or greater or 5.0 micrometers or greater or 6.0 micrometersor greater. Upper ends on these ranges are 10.0 micrometers or 12.0micrometers or 20.0 micrometers. This may be achieved on a smoothsurface.

As noted above, increasing surface roughness (discussed further below)increases the shadowing effects that create the separation of columns.FIG. 13 is a sectional view of an SPS 8YSZ-coated substrate (no bondcoatfor test purposes) where the substrate had been roughened by coarseabrasive belt sanding of the substrate prior to application of the TBC.A groove feature is shown cut by the abrasive in the substrate.

FIG. 14 is a surface view of a similarly coated substrate where thesubstrate had been roughened by abrasive belting in two orthogonaldirections. FIG. 15 is a surface view of a similarly coated substratewhere the substrate had been roughened by abrasive belting in primarilyone direction. The particular belting involved 36-mesh alumina grit on asanding belt. Force and duration were not controlled. An exemplary gritrange is at least as coarse/rough as 120-mesh or at least as coarse as80-mesh, with opposite ends of grit ranges optionally being 24- or20-mesh. When belting in two directions, exemplary directions aresubstantially transverse, preferably close to orthogonal (e.g., up to20° or 10° off orthogonal).

The FIG. 14 view shows gap widths of somewhat >0.005 inches (>125micrometers) in one direction and about 0.001 inches (25 micrometers) inthe other direction effectively forming a rectangular array of columns.

FIG. 13 also shows an opening/recess between two columns (labeled “openstructure”) of approximately 0.004 inches (100 micrometers) in widthabove the broader/wider substrate groove feature. Such open structuregaps do not appear to extend all the way to the substrate or bondcoatbut have bases at approximately even height with the feature peaks inthe substrate or bondcoat. At the bases, the coating structure may befree of columns due to the shadowing from the coating that formsadjacent the groove feature and contain a higher level of porosity. Thecoating thickness within the groove feature may also be a fraction ofthe coating thickness between grooves. The exemplary groove has a widthof about 0.01 inch (2.5 mm) and a depth of about 0.04 inch (1 mm). Thus,exemplary depth is about 20% to 50% of width. An exemplary depth rangeis about 0.20 mm to about 2.0 mm.

Thus, even without the modified spray parameters, roughening may achievesubstantially greater local separations. Progressively finer grit (andassociated roughness features on the substrate) may leave finer gaps.Thus, exemplary gap width achieved by such roughening may be up to about150 micrometers. Exemplary target gap width from roughening may be atleast 10 micrometers or at least 25.0 micrometers and upper limits maybe 125 micrometers or 150 micrometers. Desirable upper limits may beinfluenced by compromise of basic function (e.g., thermal insulation fora TBC). This may make it desirable, depending on application, to keepgap width at no more than the overall ceramic coating thickness and/ormean column width. More narrowly, limits of 25% of the thickness or 25%of the column width may be used.

In terms of synergy between modified spray parameters and roughening,different combinations may be used. In one example, a partial roughening(a fraction of the groove width observed in FIG. 13 —e.g., achieved viafiner abrasive) to leave narrower open structure widths but where columngap widths are increased to at least 4.o micrometers, preferably atleast 8.0 micrometers, with upper limits as noted above. This allows useof reduced gas flow spray parameters (e.g., Range families 1 and 3 fromTable I) to focus on increase intracolumn porosity. Another exampleinvolves such partial roughening combined with less severe sprayparameters (e.g., Range families 2 and 4) to achieve such gap width.These kinds of dual factor effects are additive and are relevant toaddress complexities in applying coatings to complex shapes where thetarget roughening or the spray parameters may not be fully realized.Additionally, combination of dual factor approaches offer capabilitythat can offset variation in the process in order to achieve gap andintracolumn porosity targets. So in essence more margin to achieve thetarget.

In further synergy situations, the same coating parameters may be usedover a broader area of the substrate than the grooving. In general, Themethods may be used over significant regions or portions of regions,typically at least 4.0 cm² or 9.0 cm². For example, on airfoil members,the methods may be used on portions of at least 10% of the area of oneor both of the pressure side or suction side or platform or shroudgaspath surface.

The use of “first”, “second”, and the like in the following claims isfor differentiation within the claim only and does not necessarilyindicate relative or absolute importance or temporal order. Similarly,the identification in a claim of one element as “first” (or the like)does not preclude such “first” element from identifying an element thatis referred to as “second” (or the like) in another claim or in thedescription.

Where a measure is given in English units followed by a parentheticalcontaining SI or other units, the parenthetical's units are a conversionand should not imply a degree of precision not found in the Englishunits.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenapplied to an existing baseline coating composition or process orbaseline component, details of such baseline may influence details ofparticular implementations. Accordingly, other embodiments are withinthe scope of the following claims.

What is claimed is:
 1. A coated substrate comprising: a substrate; and acoating system comprising: one or more ceramic layers, wherein: at leasta first layer of one of the one or more ceramic layers is a columnarlayer having as-deposited columns and intercolumn gaps; said intercolumngaps have a mean width at least one of: at least 4.0 micrometers; and atleast 1.5% of a thickness of said first layer.
 2. The coated substrateof claim 1 wherein: said intercolumn gaps have a mean width of at least4.0 micrometers over an area of at least 4.0 cm².
 3. The coatedsubstrate of claim 1 wherein: the substrate is a metallic substrate; andthe coating system comprises: a bondcoat; and said one or more ceramiclayers atop the bondcoat.
 4. The coated substrate of claim 2 wherein oneor more of: the metallic substrate is a nickel-based superalloy; thecoated metallic substrate is a gas turbine engine component; thebondcoat is an MCrAlY or an aluminide; and the first layer is a YSZ or aGSZ.
 5. The coated substrate of claim 2 wherein: the metallic substrateis a nickel-based superalloy; the coated metallic substrate is a gasturbine engine component; the bondcoat is an MCrAlY or an aluminide; andthe columnar layer is a YSZ or a GSZ.
 6. The coated substrate of claim 2wherein: the metallic substrate is a nickel-based superalloy; the coatedmetallic substrate is a gas turbine engine component; the bondcoat is anMCrAlY; and the columnar layer is a YSZ layer or a GSZ layer atop a YSZlayer.
 7. The coated substrate of claim 1 wherein: the gaps areas-sprayed gaps.
 8. The coated substrate of claim 1 wherein: theintercolumn gaps have mean depths of at least 100 micrometers; and themean gap width is 4.0 micrometers to 25.0 micrometers.
 9. The coatedsubstrate of claim 1 being a gas turbine engine component and wherein:the columnar layer is along a gaspath-facing surface of the component.10. The coated substrate of claim 1 wherein: the substrate is grooved;and the coating system has open structures above the grooves.
 11. Amethod for manufacturing the coated substrate of claim 1, the methodcomprising: applying the columnar layer by suspension plasma spray. 12.The method of claim 11 further comprising: applying a bondcoat to thesubstrate prior to the applying of the columnar layer.
 13. The method ofclaim 11 further comprising: roughening the substrate or a bondcoatthereon prior to the applying of the columnar layer.
 14. The method ofclaim 13 wherein: the roughening is an abrasive process.
 15. The methodof claim 14 wherein: the abrasive process comprises abrasive belting intwo directions.
 16. A method for using the coated substrate of claim 1,the method comprising: running the coated substrate in a gas turbineengine exposing the coated substrate to CMAS, wherein: the exposingcauses CMAS to enter the gaps and laterally infiltrate into the columnarlayer while leaving the gaps open adjacent the infiltration.
 17. Themethod of claim 16 wherein: the CMAS bridges gap openings while leavinggap portions therebelow open.
 18. A method for manufacturing a coatedsubstrate, the method comprising: abrasive roughening of the substrate;applying a bondcoat to the substrate; and applying a ceramic coatinglayer by suspension plasma spray.
 19. The method of claim 18 wherein theabrasive roughening comprises: abrasive belting directions.
 20. Themethod of claim 19 wherein the abrasive belting comprises: abrasivebelting in two directions.
 21. The method of claim 19 wherein theabrasive belting comprises: abrasive belting with a 120-mesh or coarsergrit.